The Weekend

Another weekend gone, and back to work. Not much exciting about that eh?

Managed to get in 5 flights with the Tucano and 5 flights with the TigerMoth over the weekend. Although I am almost cursing myself by putting it in print, but I am starting to get a feel for the Tucano. With the Zero out of action I have been relying on her as my go to speedster, and my new 2100mAh NiMH TX battery pack seems to have taken a lot of the glitchiness away from her flying. And this weekend I also sorted out the throttle to elevator mixing so that she now flys in a nice straight line regardless of power.

In some ways she is quite a bit more fun to fly than the Zero. Although the Zero has a better power to weight ratio and better vertical performance, I think the Tucano is a fraction faster in a straight line. Add to that she has a whopping rudder, unlike the Zero's piddly after thought and she is quite a capable aerobat. The one manuveur I really haven't been able to figure out how to do on her is a knife edge. Rudder deflections with the wings perpendicular to the ground just make her fall over onto her back.

One issue that did come up with the Tucano on the weekend was that once again the engine leads had moved so that the motor was wearing against the insulation. I noticed the decrease in performance on the first flight on Sunday. Left untreated I know that this eventually causes a blown ESC from previous experience. Fortunately the fix was easy, just secure the ESC further back so that the leads are pulled away from the engine.

DJ maidened his brand new Ultimate Biplane on the weekend with, for the most part, good results.

Interesting plane. 25 Amp brushless motor and ESC are included in the package. Motor is a direct drive outrunner spinning a 10x7 prop if memory serves. Fully symmetric wing. Big big control surfaces.

Anyway, good takeoff and away, nice first flight, all things considered looks like a very nice bird. Not sure why, but the motor does introduce a lot of vibration and as a result it makes a surprising amount of noise for an electric with a low kv motor. Quite a cool sound in many respects given how often these things work out to be way to quiet.

On the second flight of Ultimate there was an "incident". A loop that didn't really complete before altitude 0. Fortunately it was 99% complete, and so some bent undercarriage, and broken firewall and a few other loose fittings were the only problems out of what could have been a monster crash.

I probably haven't mentioned on the blog that a mate took me for a ride in a light aircraft over Canberra recently. While we were up there I managed to snap this shot of the our Kambah field from the air.

That big bit of black in the middle of the field is our bitumen area. It looks kind of big from the air doesn't it - seems harder to hit in real life than that.

Tiger Moth had four batteries put through her on the weekend. Considering how bent she is, and the fact that I am constantly having to trim her I continue to enjoy just trying to fly her in the most crazy ways possible. She is so bent I really don't think I can be bothered putting a brushless in her, but by the same token I know it would make her even more interesting. I also on Saturday flew her quite happily in a box bounded by the the bitumen area - she is that slow. The only time I flew outside the box was for approach, and even then it wasn't far away.

Finally to the bit of irritation for the weekend (it wouldn't be model aviation without irritation). I've finished the airframe for my PLD Microseether and was hoping to have her maidened over the weekend. I've had all the necessary avionics weeks in advance, so on Friday night was hoping it would all go together in a couple of hours. But it was not to be.

The microseether is a pusher designed really for one particular motor - the GWS 2205 outrunner. Like many outrunners the 2205 has a reversible prop shaft so you can mount the face as the part that doesn't rotate, or the base as the part that doesn't rotate. My motor was setup the wrong way, and the grub screw so tightly secured that I stripped it when trying to get it undone. Have tried a couple of things across the weekend to get it undone (with thanks to Crawf and Inflex for suggestions) but with no effect. Don't know whether I should just order another motor, or what.

Anyway, as Pete Cundall might say if he were a model aviatior, that's your zoomin lot (and you thought the bad puns were gone forever didn't you?).

What's going on

Just came back from a glorious morning's flying. Was a quick one as work and other such "real life" events are unfortunately getting in the way, but what a glorious morning.

The sun was up and shining brightly. The ground was cold and frosty, but it was dead still. That often takes people by surprise about Canberra. The reward for enduring one of the really cold nights is often a beautiful bright, sunny, warmish, alpine winter's day.

I put up my GWS Mini Dragonfly first. She now has her new superskids, and a new 2s 1300 mAh battery courtesy of NQRC (when I say courtesy, I did pay for it, although Paul Daniels from NQRC did very kindly replace my 3s 2200mAh that went in with the RV4 at cost price when he heard about my misfortune, which was a lovely gesture). The new battery had the MDF ready to lift off at around the half throttle mark.

Today I tried to keep her in the air for longer with mixed results. Although still struggling for control I put her in for a few controlled "crashes" although I did go in heavy by the boom at one stage and broke the boom, but not a clean snap through. It could have been worse - I realised what I was doing (pulling back on the cyclic pitch - the "elevator") and pushed forwards in time to stop her landing only on the boom.

After that the boom, although broken, looked strong enough to fly. Of course, even though the boom could support its own weight on the ground I of course forgot to consider that in the air it has the added force of the tail rotor acting on it. Once I had her in the air and semi-stable I realised the tail boom was handing down behind the heli at like a 30 degree angle of deflection - oh dear. Brought her in to land - no probs.

The super skids are awesome. They turn hardish landings into a non-event.

Tucano was next on the flight line. With the Zero out of commission we borrowed the Zero's multiplex battery (which I must review sometime) and had a nice relaxing flight with her (yes - relaxing - with the Tucano). When she isn't glitching she is actually quite a lot of fun to fly. Today I was working on hammerheads, nice long loops etc. I must try some knife edges again, but haven't found them all that easy to do with this plane.

A great flight was followed by a great landing in still conditions. I've concluded flaperons are a real mixed blessing - they give you a very slightly lower stall speed, but at the same time unless they are perfectly setup they throw your plane out of trim, and you end up having to compensate with aileron as well while landing. I think the Tucano is easier just to bring in hot with no flaperon, let her flare for a long long time with the power off until she just touches down. It takes a little more planning to hit the landing area, but with her smart undercarriage, going long onto grass isn't an issue (going long into the ditch is another matter).

The Tigermoth had a spin. I've figured out how to snap roll her, and she looks beaut doing it. I just wish my girl wasn't quite so bent - her injuries from my inept flying plus radio issues at the start of my flying career have left her permanently scarred and basically impossible to trim. This comes through particularly as she changes angle of attack at speed. Her right wing, which obviously has more flexible hot glues joints in it, bends up a little more than the left and she puts herself into a right hand roll. Oh well - maybe one day I will buy a new airframe, but probably not.

Other RC news. My Microseether is coming along gradually. Nice little kit with excellent instructions. Also - the full kit is the full kit. Excluding avionics/motor there is nothing more to buy. It even comes with covering. I'll do more of a writeup once she is done.

I sat down with the RV4 wing last night to start the job of rebuilding her. The wing was the least damaged part (although ironicially it took the impact of the mid-air, and the damage to it was what crippled the RV4). Boy - what have I left myself in for here. I was expecting the wing to take about an hour to repair. However, I was expecting the balsa spars to still be in place, just broken, but all the pieces to be intact. Unfortunately, not that easy. Damage to the leading edge and two of the three spars on the top of the wing will require complete replacement of that section. All very doable, provided I can find the balsa for it.

Sorry - no photos for this post. Maybe next time.

Learning to Fly Part 10 - Silver Wings

Learning to Fly Part 10 - Silver Wings

Prerequisites: You've taken your first couple of flights with your new aileron plane. You've done plenty of practice on the simulator.

Objectives: Not much really, I'm just going to chat about some stuff I think that maybe you need to know.

If you've gotten this far then congratulations. If your aileron plane is flying safely, and your rolling landings are successful then you have bascially completed the objectives of this course. What I might try and do is talk about a whole host of tidbits of information that you might find useful in the rest of your model aviation pursuit.

Time for a New Type of Plane

When are you ready for your next type of plane? It's a difficult question and it can come up for lots of reasons. Sometimes a model is smashed beyond repair and decide to replace it with something different, maybe you have become bored with the flying envelope of a model and want to try something else, or even you are convinced a model is not a good flyer and feel a diffierent model would give you a better chance of mastering model flying.

• Only you can tell when you are ready for a new type of model, but the people you fly with (if there are any) can tell when you are not ready for a new model. Ask the ones you respect for their opinon.
  
• If your old model never flew well be honest with yourself and make sure it wasn't because you chose a model too advanced for you.
• Before you move on it is best to have competence with your aileron trainer. After that you can set your own pace (well you can now as well I spose).
• When you look at a new model be realistic about whether you are ready for it yet. Push yourself a little perhaps, but don't push yourself too much.
  

There are all sorts of possibilities that open up to you after you have taken the time to learn to fly your aileron trainer well - scale flying, aerobatics and pattern, 3D, high speed, or just tooling around the park enjoying the sheer pleasure of any sort of RC flight. The best of luck to you with the next model after this one (and the one after that [and the one after that]).

Flying in Adverse Conditions

Unfortunately not every day is a perfect flying day (today for example, as I write this rather than flying). When is it good enough to go out, and when is it not? As usual, no definitives answers from me (handy isn't it).

Try more and more adverse conditions at a pace that you are happy with and don't risk your most breakable models in weather you haven't flown in.

Here's a few tips:

• A strong steady breeze is quite manageable generally, but a gusty breeze can make flying risky.
• Keep your model upwind if flying in a strong breeze.
• Avoid parts of the field where the wind goes around/over/through significant obstancles (like a row of trees) - you often get wind sheer, eddies and other air disturbances in these areas.
• Make sure you land well before your battery is depleted. Having control authority and power is critical to staying safe.
• Make sure the model is appropriate. Models with very light wing loading (like Slow Stick, Pico Stick) and to a lesser extent models with very high drag (like Tigermoth) are not appropriate for adverse weather. Models which aren't well powered and capable of flying faster than the wind speed are also out.

Confidence Versus Ability

If you have learnt how to drive, and that was a few years ago now then you may have experienced the effect where your confidence increased faster than your abilities. Looking back you may realise that some of the "incidents" you found yourself in you survived more through good luck than good management (although at the time you may well have chalked it up to good management, further increasing unjustified confidence).

The same thing can happen with RC flying (fortunately overconfidence in the air normally just results in a bruised ego and thinning wallet). If you fly, and nothing goes wrong, your confidence is naturally going to increase. If however, you have a few problems along the way, chances are that you are going to have somewhat adjusted your confidence to your ability.

Overconfidence in RC flying normally, in my experience, results in:

• Pilots flying too close to the ground.
• Attempting aerobatics too close to the ground.
• Trying to fly models that are well beyond their ability.
• Not bothering with checks (control throws are the right deflection and direction, radio checks etc)
  

I had a situation just like this myself the other day. I rolled a plane I was maidening on its back for inverted, even though this was its first flight, from only 10 metres up. I didn't have enough elevator authority, or time to roll her back, and she went in.

Now, there's no soapbox here. I've skipped checks myself, and it didn't caused me a problem, but then I've had crashes that if I'd done my normal checks I would have avoided, and had situations I would have recovered from if I followed my own rules (like the plane going in above - 10 metres, on a plane I didn't know the flight envelope of - what was I thinking).

So, as you go forwards, be aware of the difference between your confidence level and your ability.

Landings

Every landing involves two things that demand your attention:

1. Your aircraft's altitude goes from a safe flying one, to ground level.
2. Your aircraft's velocity goes from one that enables flight, to zero.

A good landing is one where the rate at which altitude and velocity change is such that the aircraft is undamaged by the transition.

Sounds like gobbeldy gook - perhaps, but the point is that the difference between a good landing, and a broken model is not that much.

For the reasons above landings are always somewhat risky, and unless you are super gifted they deserve your respect and full attention, and will for some time (probably forever). Tell the people talking to you to shut up (nicely! - or just block them out if you can) so that you can focus on the job at hand (unless of course the person talking to you is giving you landing instruction - with your permission - otherwise really tell them to shut up 8-).

Once you've got the basics of flying your aileron plane sorted, start to get lots of practice landing it. You can easily do 3 or 4 landings on every battery and still have some juice for fun, and the focussed practice on landing will turn these moments of terror into times that you know are risky, but very doable provided you focus.

One more thing, as you get used to power approaches and landings don't forget your dead stick landings because one day it will happen for you. On powered approaches you control the rate of descent with the throttle. On dead stick approaches you dive below the glide angle so you have enough airspeed to flare.

Interference, Mistakes and Other Flying Incidents

You do this hobby sooner or later you are going to have a crash. If you taught yourself to fly then chances are you've already had a few, but as you move onto different models the effects of crashes will almost certainly be worse. Trainers are tough, and don't tend to go in at full tilt because of their self correcting nature.

There are many things that can start the path towards a crash, but one thing is consistent - a crash ends with an aircraft striking an object or the ground. Hence, if you can stay away from objects (including the flying kind) your chances of a glitch, temporary loss of orientation, wind gust, solar flare, flameout, collision etc taking out your model are reduced.

Now contrary to what has been suggested through the course, this relationships with the ground and altitude is not fixed. For lots of reasons (see below) being close to the ground becomes more risky as you get further and further away. The diagram at the right attempts to illustrate this (and yes I did think long and hard before labelling the area close to the ground the "Danger Zone" for fear it would send Top Gun fans flying straight for it).

As your model gets further away from you:

• It is more likely to take an interference hit.
• It is harder to see leading to a more likely loss or orientation. This applies to depth perception as well - once your model is far enough away it is really hard to tell if it is in front of, or behind that tree/light pole.
  
• It will be harder to land if you suffer a power failure.

The odds of surviving each of these situations will be improved if you have altitude (or clearance in the case of an obstacle like a tree or light post). Altitude gives you time to recover from a loss of orientation or glitch, and if you lose power, you have a chance to get the model somewhere back close to you to land.

Now, I don't know if the numbers I've given in the diagram are entirely accurate. Maybe you can go out to 100 metres before you need 15 metres of altitude, but the idea is that the safe area to fly your model is cone shaped, and it gets higher as you get further away. Can you fly below it - of course you can, but you are increasing the risk of an incident taking out your plane.

Having lost power at 100 metres with only 5 metres of altitude, on a small park flyer, my experience is that the fate of your model is in the hands of the gods, because you can't see well enough to do anything particularly meaingful.

Flying Attitude

As I've written these pieces I have the awful feeling that I've probably come on a bit strong with the fire and brimstone stuff. I've tried to never say though shalt not, although I'm sure that meaning could often be inferred from my words.

Allan Kirk, from NZ Motor Cycle Safety Consultants, who I have a great deal of respect for, speaks, in relation to motorcycling (another past time of mine) about the idea of a child and an adult riding a motorcycle.

The child is adventurous, enthusiastic, passionate, curious and brash, while the adult is cautious, pragmatic, rationale and reserved. The key to enjoying what you are doing, but doing it safely is being able to be the child when the conditions are right, but being able to switch back to the adult immediatelly when you have to.

In many ways I think it is a great way to think about RC flying. My own handle "ozrcboy" was a reflection of how this hobby made me excited like a child again - a feeling I thought I had lost (don't worry we aren't about to go psychoanalytical).

At the end of the day my opinion is that the only absolute duty you owe in your flying is to take reasonable steps to ensure you don't harm others or their property. This is the time that you must be the adult. The rest of the time, you are probably going to take some risks to learn and to enjoy yourself. As long as the only thing you are risking is your aircraft (and ego and wallet) you can leave the child in charge as long as you wish. But, as soon as the propect of actual harm to others, or their property is present then you need to let the adult take over. There is also nothing wrong with letting the adult set limits that the child is allowed to play within - you can do anything you like above 10 metres, you can fly fly upside down at any altitude as long as it is in that area, etc.

The only other things I want to mention are persistence and resilience. You will suffer some setbacks. While you are still enjoying it keep at it. Let the adult figure out what went wrong, and set new boundaries for the child, until they can be relaxed again.

Conclusion

This is the last of the course. Congratulations on coming this far. It always makes my day to get notes from people who have found these notes useful, so please, don't be shy. Likewise, I always find it useful to hear from people who think my notes are wrong for some reason, so likewise, let me know. You can either email me ozrcboy@gmail.com or use the comment button below.

I wish you all the best for your model aviation future.

Cheers,
Oz

Back to learning to fly.

Back to main.

Oh man..., not again

You fly RC you had better get used to the occasional (and sometimes more than occasional) dissapointment. Yep, she went in again this morning.

I'd just engaged GroundDancer in a race with his Typhoon (which alarmingly he won, although I didn't have my best battery on the job). I flew a circuit or two more - went high power to see what sort of vertical performance I still had, and got a message to land from the plane.

Now - at the start of this process I was only about 5 metres from the ground, so I didn't have much space to play with. I sent the plane away from myself, giving her WOT to try and make her climb, but this battery was spent. With the plane just 1.5 metres of the ground about 40 metres downwind from me, and me knowing I didn't have enough airspeed or power I was just about to start a deadstick downwind approach. That's when the glitch grabbed her and threw her into the ground.

She had been glitching about a bit in the air a bit, but of course losing a metre of two of altitude - no problems providing you have 2+ metres of altitude to play with. The question might be in your mind reader so let me put this out there - she didn't stall, she had enough airspeed. In fact the damage she sustained showed that she was well above stall speed (and no the wind wasn't so strong it would account for the difference).

I was surprised at how damaged she was as it didn't seem like a big impact - she had enough speed to fly but not excessive - I guess the glitch must have really driven her into the ground. You may also recall on the last rebuild I noted that the foam is starting to seem quite brittle - maybe exposure to UV. Although she looks badly banged up she should repair okay - clean crack through the fuse, reglue the wing retainer bolt, re epoxy the firewall. However, there were two bits of damage I haven't seen before - one of the aileron torque rods has punched up through its aileron - should fix up okay with some epoxy, and one of the undercarriage wires has sheared off at the wing - from the photos it looks like the wheel was still on at that stage (and I don't remember seeing the wheel at the "crash site") so it must have dropped off at some stage afterwards - hopefully it is in the back seat of the car (I seem to remember the wing resting the way it should on the seat). Hopefully I can find that - I think this old bird is a little too fragile to start belly landing her at this stage.

RC Schemes

Few things on the go at the moment.

Have a new flat profile P38 Lightning from Wattsuprc. I'm going to strap two 1800kv ewatts motors to it with some 5.5x4.5 props. My estimate is I should have a pitch speed in the order or 110km/hr and somewhere around 800grams of thrust. Having just looked over a fair bit of the thrust/pitch speed stuff it was an opportune time for a two engine model to come along as I now understand the advantages - you can have a higher pitch speed and slightly less thrust on each motor, because you get to combine the thrust. Easy enough eh? Only thing that is a bit of a worry is how a flatout will handle the speed. I'm actually expecting it to be quite a high drag airframe based on what I know of flatouts. All the same though, if it reaches 100km/hr and embarrasses some more Strykers I'll be more than happy.

Some superskids are coming for my GWS Mini Dragonfly to replace the stock undercarriage. Most of the Mini DF is pretty well laid out but the stock landing gear is a real weak point. Speaking of the Mini DF I've decided the honey bee I was using on clearview was way too easy to fly compared to my experience with the MDF. So, I took some advice from Paul Daniels at NQRC and have been practising using the GWS Mini Dragonfly in FMS. Setup with 0.2 m/s wind and 0.2 m/s gusts it is taking a lot of concentration and work to keep her in the air - feeling much more like the real thing so I will keep at it.

I have a busted up supercub that is in need of repair. One of the flyers at Lyneham put her in, and when the pilot indicated he was going to throw out the airframe I asked if I could have it. I don't think it is that badly damaged and plan to set her up with an ewatts 1200kv motor (I know, my entire fleet seems to run on ewatts motors) with an 8x4 prop - should get about 600 grams of thrust with pitch speed around 50km/hr. Should fly well.

I've started work on the PLD Microseether. I'm taking photos along the way so I'll do a post about the whole process at the end. For the most part straight forward build although there is a little more sanding and shaping of the wing than I might care for. However, I spose that is the way it goes with solid balsa wings.

Great conditions across the weekend. Plenty of flying in with the usual suspects. Haven't been out to Lyneham recently though. The visit out there by the Environmental Protection Agency last week has many worried about the merits of flying with so many others. To be honest, was getting a bit crazy out there with respect to frequency clashes etc.

Controlling the Costs of RC Flying

I've just placed an order for a couple of hundred dollars on a vendors site, and it occurs to me that it worth talking about how to control the costs of RC Flying. After all, while all of us have a pretty strong emotional attachment to the hobby, meaning we don't always make particularly sane purchases, I'm sure we all recognise that a lower cost per model means less aggravation with the finances, or maybe even more models 8-).

Here are some things I do:

1. Favour models in the 300-600 gram (11-22 ounces) range. I know I can get a good brushless setup for such a model for around $45 AUD including motor and speedie. There are a ton of cheap brushless motors and speedies provided you don't want any more than about 170 watts, which will fly a 400g speedster, or a 600g trainer very well. If you step up to around 200 watts suddenly the combined price comes up to around $80-120AUD. In addition, 300-600gram planes all tend to use standard micro servers (7-9grams) allowing another saving by using cheap servos if appropriate. Finally, lighter planes tend to have less serious accidents. Although airframes are often ruined and LiPos and motors sometimes damaged/destroyed normally these components survive in lighter planes.
   
2. Before I buy a new model I try to figure out whether any of your existing LiPos will fit it. One small problem with the GWS Zero for example, is how thin a 3s needs to be to fit the battery compartment. They are typically slightly more expensive batteries.
3. I use cheap servos in models where a crash wont be the end of the world. Hitech HS55s are a bit of a defacto standard for micro servers, but the truth is you can save half the cost of the servos for your plane by using cheaper servos like the Esky and JP Energe servos. My experience with these servos indicates they have good long life, and work just fine. For example, my 200+ flight GWS Zero is using two JP Energe servos.
4. As much as possible standardise on LiPos across the fleet. This is a bit of advice I haven't followed all that well which is a bit daft. If you have a battery for each plane, then a crash on that plane renders some part of your LiPo fleet useless. If you have a couple of common LiPo types you can just fly other planes more.
5. Fly further from the ground - heh accidents happen, glitches happen, things go wrong. If I spend my whole day messing around at 2 to 3 metres the odds of one of these events nabbing a plane is much higher than if I tend to fly in the 5 to 10 metre range most of the time.
6. Balance my LiPos - I wasn't a convert, but now I am. Balance your LiPos. They will last longer. Remember - electric flight isn't free - it is the cost of the LiPo divided by the number of cycles it will live for. If I balance it will increase the number of cycles in most cases.
7. When I buy an airframe I consider the repairability. For example, GWS, Multiplex and many other foam birds repair well. Parkzone Typhoons and Supercubs repair well. Balsa and ARF Balsa are sometimes repairable on bad crashes. However PZ warbirds tend to disintegrate on bad crashes and need to have the airframe replaced.
8. Check the amp draw on my engine setup. Overdrawing the LiPo will reduce its life. If the speedie or motor is constantly abused it will reduce their lives. Worst case I could lock out the speedie, lose the BEC, and then lose the whole aircraft. If I am going to abuse the equipment limits, I like to know by how much I am abusing them.

That's all I can think of at the moment. I'll add to the list if other stuff comes to me.

RC Articles

Stuff I've written that is more than just blog ramblings...

Learning to fly:

1. Teaching yourself to fly fixed wing RC - the Ozrcflying course.
2. How to do successful hand launches - maybe read this one before your first attempt.
   
3. Learning how to fly RC Helicopters (Radd's School of Rotary Flight - external)
4. Tips and Tricks - for once you have completed beginners.
5. One Page Guide For Learning To Fly Warbirds - For Novices
   

Checklists:

1. Takeoff Checklist for Electric Parkflyers
2. The Maiden Checklist - Tips to help your new bird survive more than one flight.
   

Technical:

1. An introduction to the basic electrics of electric flight
2. Thrust, pitch speed, and model speed - Understanding these relationships.
   
3. The Glossary - Don't know what a term means. Look it up.
4. Controlling Risk When Charging LiPos - take a look at my solution.
5. Prop Unloading - Fact or Fiction - a work in progress as I try to understand what causes this phenomenon.
6. A Guide to Electric Flying for Nitro/Glow Flyers - like the Hitchhiker's Guide says... "Don't Panic".
7. Useful guide to sizing electric power systems on wattflyer.
8. Some Basic aerodynamics.
9. Magic Numbers for Electrics - excellent background knowledge for once you have the basics of electrics down.
   

Reviews/Gear/Planes

1. The Hangar - see my models old and new.
2. Gear Reviews - what I thought of various bits of kit.
3. Review: Electrafun XP (Current and Original - read the current first in my opinion).
4. Programming TowerPro Mag8 Brushless Speed Controllers - if yours came without instructions this may help.
5. Review: Stevensaero RV4
   

Modelling Tricks/Tools/Techniques

1. Undercarriage Mod for GWS TigerMoth 400
2. One approach to mounting a brushless outrunner in a GWS Warbird
3. First Scratch Build - The Multi-role Micro Ultra Stick
   

Opinions, Articles etc (more than just reports on my flying)

1. Building to Fly or Building to Crash - an opinion, and one that is kind of controversial.
2. Controlling the Costs of RC Flying - making your dollars go further.
3. FMS Downloads - A modified supercub that is like a hobbyzone Supercub is here amongst other things.
4. Getting your plane out of the tree - what works for me, and what I've heard others suggest.
   

Funnies

1. Get Your Ground Glider Here
2. The Immutable Laws of Model Aviation

Understanding More About Electric Flight

If you read through the "Basics of Electric Flight" it may well have left you wanting more information on how to size engines for speed/thrust etc when designing and building your model plane. So, here is some more great stuff that helpful people in the hobby have taught me, or I have figured out myself.

First some basics:

Pitch Speed

Pitch speed is the speed of the engine/prop combination through the air ignoring drag and prop slippage.

It is simply based on the multiplying the pitch of the propellor, by some number of revolutions for a unit of time.

For example lets say we have a 7x5 prop that we know is being driven at 10,000 rpm then the pitch speed of this model is 50,000 inches per minute (5 from prop pitch multiplied by 10,000 rpm). Once you have this number, conversion to more useful units (such as km/hr or mph) is just a matter of multiplying by the right constant value.

To get km/hr, multiply by 0.001524
To get mph, multiply by 0.000947

So for the example above, with the motor spinning at 10,000rpm, the pitch speed would be 76km/hr or 47mph.

How do you find the RPM? Many motor manufacturers will publish this information with their engine. Some don't. If you don't have published information you can often take an educated guess by looking at the recommended prop ranges for a motor, and assuming that the smallest published size will spin the motor at approximately 85% of kv * volts (so a 2000kv motor with 11.1v, you would expect appoximately 19,000rpm. With the mid range prop you would probably expect around 70% of kv*volts (so 15,500rpm from the example above), and with the largest recommended prop maybe 50-55% (so 12,000rpm from the example).

The best way to find the RPM if it isn't published is to actually measure it with a tachometer.

Finally, if you have an inrunner which is reduced through a gearbox before spinnning the prop you of course need to factor that into your calculations. For example, a 3000kv motor reduced through a 3:1 gearbox has an effective prop kv of 1000.

Thrust

Thrust is a measure of the force generated by an engine/prop combination. Typically it is expressed either in ounces or grams (and those of you that know your SI units of course realise that grams is a mass, not a force, and that this should be more properly described as grams at earth gravity).

Typically a wider diametre propellor will generate more thrust, to a point. Perhaps you have already noticed the tradeoff here. You generally get higher pitch speeds with a smaller prop, but you generally get more thrust with a larger prop.

If you engine doesn't have thrust info provided with it, then you have to figure it out for yourself by measuring it. You'll need some sort of rig that allows you to measure the force the engine generates at full throttle.

Air Resistance/Drag

All things that move through a gaseous medium (ie air) must overcome air resistance. Aircraft are no exception, and they are further affected in this regard because their wings create additional drag.

The important things you need to know about air resistance is that its relationships to velocity is a squared one. That means that if you double your speed, your wind resistance increases by a factor of four. For example if your wind resistance at 30km/hr is 100grams, then your wind resistance at 60km/hr will be 400grams, and at 120km/hr will be 1,600grams.

So How Fast Can a Model Go?

As a model accelerates the amount of drag increases as square of the velocity until either drag equals engine thrust, at which stage the plane will stop accelerating, or the plane reaches the pitch speed of the prop, at which stage it stops accelerating.

It's a bit like gearing in a motor car. In first gear, you are "pitch speed" limited. You have plenty of power to overcome wind resistance, but eventually you reach a point where the engine is at red line and can't (safely anyway) spin any faster. However, it top gear you tend to be drag limited - you accelerate to a point where wind resistance equals the acceleration the engine is providing and you have reached your top speed.

So, the plane's top speed is governed by the lower of the point where thrust and drag intersect, or pitch speed. The graphs at the right will hopefully illustrate this - click on them for a blown up version.

The upward curve is the "drag line", the blue line is the "thrust line" and the yellow line shows the pitch speed. All of these graphs are based loosely around the ewatts R2212 and R2282 1500 and 1200kv motors, with various airframes. For example, I think the first one pretty closely matches my GWS Zero performance.


Choosing the Right Motor/Prop for Your Model

Of course it does depend what your application is. If all you want is thrust for 3d work you are better off getting a lower KV motor and using a larger diametre prop - you are getting the most thrust you can, but typically paying for it with pitch speed (a bit like the 9x3.8 graph). Also, if you have a slow flying airframe you often need to pay for this in terms of drag as you try to go faster.

If you are after speed you have to make a compromise. Clearly you want pitch speed, but you also need enough thrust to overcome air resistance. Normally you have to trade pitch speed against thrust. Sometimes it is easier to lower the air resistance of your model than increase the power (more on that later) if you want it to go faster.

Going Faster

So something I have seen come up on forums from time to time is something along the lines of "this guy showed up with *some fast plane* and blew away my *I thought it was fast plane*. I need to upgrade my power so that I can blow him away."

Okay - time for some hard numbers. As mentioned above, drag increases as a square of velocity. So, to go twice as fast you need four times as much thrust (ignoring pitch speed for the moment).

Let's say for example that you use 700grams of thrust to go 90km/hr, and decide that you need to catch a plane that can fly in level flight at 110km/hr. Take a guess at how many grams of thrust you need (ignoring pitch speed as a limiter for the moment). Got your guess ready? 1050grams. That's right, 50% again to increase your speed by 20km/hr.

Unfortunately Mr Newton has more unpleasantness ready for us. Power is a measure of work over time. If we want to fly twice as fast we need four times as much work done (because we need four times the thrust from above) being done twice as quickly. Yes - you need 8 times the power to go twice as fast. So let's say you were using 200watts to get 90km/hr, what would your power requirements be at 110km/hr? Got your guess ready... were you anywhere near 365watts?

Now - don't despair. A power system upgrade can be a fine thing at times like this, but in many ways you will probably get a much better return by reducing the drag coefficient of your model.

For example, if you reduce your drag coefficient by 20% you can fly a linear 20% faster for the same amount of thrust. So, in the example above you would have almost gotten to 110km/hr without putting in a single watt more of power.

The graph on the right shows another example of this concept.

Now, reducing the drag coeffecient of your model (by reducing wing area, reducing the size of the airfoil etc) is not a free ride by any means. You will end up with a higher stall speed amongst other things making landings and takeoffs more difficult. Your model may well become unstable, you could change the centre of gravity etc. In so many ways you could ruin a great plane - but you could go a bit faster too. So, if you want to make your stryker go faster, as well as upgrading the power, think about how you can reduce the drag coefficient.

What about Weight - Doesn't It Affect Speed?

As best I can tell, weight does not affect straightline speed in an aircraft. It affects acceleration, but not top speed. Obviously if you are fighting gravity then mass does make a difference.

How Do I Tell Whether My Speed Is Pitch of Thurst Limited?

If a model is severely pitch limited it is usally pretty obvious - you push the model to full throttle, it jumps very quickly to a speed but then just stays there. The model has plenty of thrust, but just wont go any faster.

If the model takes a little time to wind out to top speed (not ages, just some time), and can go significantly faster in a steep dive it is probably thrust limited.

If in a dive the model doesn't pick up significantly more speed it might be thrust or pitch limited, but it is so close to pitch speed that it almost doesn't matter (the model doesn't pick up much speed because once the model passes its pitch speed in a diver the propellor starts acting as a brake).

So Is It Better To Be Thrust of Pitch Speed Limited?

It really does depend on application. 3d planes are often pitch speed limited - they usually just want buckets of thrust for unlimited vertical. Most scale models fly best with thrust limited setups in my opinion.


Well I hope you found that interesting. I really enjoyed getting my head around this stuff as I wrote it. Definitely will be including significant drag reduction as part of the elebee project phase III.

Learning to Fly Part 9 - The Possibilities of Flight

Prerequisites: You have complete mastery of your trainer. You go around again on a landing approach when you realise you are going to have to walk more than 10 metres to retrieve your plane. Most of the time you land within 5-10 metres of yourself. You've bought yourself an aileron plane from the list previous.

Objectives: Coming to terms with your new plane, getting your new plane ready to fly, flying it, learning what it can do, and how to stay out of trouble with it and simulator exercises with your new plane.

Coming to terms with your new plane

So this time, when the instructions said you'll be flying in 30 minutes (once the battery charges) it's okay to just go out and fly it? Well, you make your own choices, I would recommend against it. Your aileron plane is going to be very different to your trainer.

And probably the best place to get familiarity with a new plane is in a simulator. Just recapping your simulator options. FMS is a free one but there are plenty of others from quite cheap (like Clearview at $30USD) all the way through to somewhat expensive (like RealFlight at somewhere in the $300-400AUD range). Once you have the sim you need to get a model for it that will vaguely match your plane.

I've put together a few more models to try and match some of the planes I suggested in Part 8 on the FMS download page. None of them will be exactly like your plane and they are all intended more just to give you an idea of aileron flying. In addition there are plenty of resources on the net for more FMS models.

I haven't been able to find models that match all of the planes I have suggested unfortunately, so you will have to make some allowances. Try and find one that is kind of close to the aileron model you have choosen, either here or elsewhere. Fly the pants off it in the sim, have fun - do the crazy stuff, but also do the basics like nice clean takeoffs, controlled circuits and landings. Practice your landings a couple more times, maybe a little more landing practice. Then, grab some other aileron planes and do the same thing. Get a feel for how different aircraft work, from the thin winged aerobats, through to the low wing warbirds, and the high wing cessnas etc.

So What's the Big Deal Anyway?

Ailerons make a plane roll, as does the rudder on a plane with a high dihedral wings, so the control does the same thing, so why all the fuss (aka why can't I have my Spitfire yet)?

Probably the biggest single difference is what happens when you over control the different types of aircraft. A rudder plane with high dihedral self-corrects to a point, and if you go past the 90 degree (perpendicular to the ground) with the wings it folds over into a stall which is easily recovered from by just putting in up elevator.

In contrast, if you roll an aileron plane past 90 degrees it doesn't fall into a stall. It stays at the orientation you put it in, whilst rapidly heading towards the ground. Correction is a two phase operation - you need to correct the roll (because it wont do that itself) and then restore level flight. Sometimes, if you are really close to the ground, you need to use down elevator (because the plane is partially inverted) to buy enough time to roll her back. In this situation you need to make the right call on which way to use the elevator based on whether the plane is upside down, or the right way. Go the wrong way, and you nose the plane in hard.

RET (Rudder Elevator Throttle) planes also lose less altitude in corners than REAT (same as RET + Ailerons). By now you should have a pretty well coordinated rudder/elevator thing happening on corners, so that shouldn't be so much of an issue for you, but I spose it is another good reason for beginners who aren't getting assistance to stay away from REAT planes.

Ailerons also allow you to try many more risky flying manuveurs. No problems provided you plan for them with the usual altitude allowance.

Getting It Together

If you've bought an ARF then you need to get her together before flying. Building an aircraft can be quite daunting the first time. I myself have never been particularly skilled with fine work, but the good news is that if I can do it, anyone can.

Here are a few hints:

1. Light planes fly better. Do everything you can to keep the weight under control. Use glue sparingly, particularly aft of the avionics bay - the tail in particular must be as light as possible (the tail is about 4 times as far from the CoG as the nose - any weight at the tail needs to be counterbalanced by 4 times the weight in the nose).
2. Be gentle, but don't be paranoid. Yes planes can be broken easily, and if you break something you may well think that is the end of the model - don't despair - gravity will probably do far worse things to your model - almost every situation is recoverable.
3. Don't worry about how long it takes you to put together your first ARF - just do it at a speed that you are comfortable with. Normally if you spread the build over a few nights you will get a better result than if you try and do it all in one hit.
4. Buy the battery for your plane before/at the same time you buy your aircraft, and make sure the battery fits the compartment before you glues the fuse halves together (if that is how your kit works).
5. Look through (I hesitate to say read given the quality of the english in some of them) the instructions a few times before beginning the build.
6. Make sure you get your CoG right. I know that adding weight to a plane at the nose feels like drinking a decafe latte with soy milk - it's just not right - but if she isn't properly balanced she will be hard to control, and you will probably put her in.
   
7. Try and make the plane as straight as you can. A small plastic set square (like the one you used for geometry at school) and a dressmakers measuring tape will both help in this. It doesn't have to be perfectly straight to fly well, but by the same token, it is hard for it to be "too" straight.

Flying your new plane

So, let's start at the end with landing:

Your REAT plane will probably land best when she approaches under power, and lands under power. This may be a significant departure from the way you did things with your trainer.

Most REAT planes are not going to have as low a wing loading as your trainer (see the glossary). This roughly means they will either need to fly faster than your trainer to stay airborne (such as the extrafun/Zero), or will have a high drag wing to create more lift (Tigermoth). In both these cases, for different reasons, having power to land and approach will make things easier.

We talked about how to do powered approaches and landings in part 8, but just to quickly refresh on them:

• Don't dive below the glide angle, set the throttle so that the aircraft is losing altitude, and use the elevator to push the nose down if she is going too slow and might stall, or pull the nose up if she is going a bit fast.
• Just like a power off approach you flare as you get close to the ground. What you do with the throttle at this stage depends on the approach. If you are going too fast, you can close the throttle. If you are losing altitude too quickly you can add one click of throttle (maybe two - anything more and you are going around). If everything seems just perfect, you can hold the throttle exactly where it is (provided you aren't belly landing) and close the throttle the instant after she touches the ground.

How your model slows down will depend on the model. The high drag airframes like the Tigermoth will just bleed velocity very quickly once you take the power off. Slicker airframes like the Zero, Extrafun and Stryker all need time and distance to get rid of airspeed (btw - the Stryker can be glided in for landing power off just like a trainer - don't bother trying a powered approach with her, it wont work particularly well (be very careful of your airspeed if you bank with the power off though - if you stall the inner wing you are screwed).

Now, we have often talked about the importance of a good approach to achieveing a good landing, without necessarily providing much advice on how a good approach is put together. If you have been flying away from yourself, getting the altitude about right, and then turning 180 degrees to come back and land you haven't been doing things the easiest possible way (so why didn't I tell you earlier 8-) because there is already a heck of a lot of "stuff" in these articles). The easiest way to put together a good approach is to fly a three leg approach - downwind, base, and final. The diagram at the right should explain most of it. There is not a heck of a lot more to say about it except that you will need to experiment with it to get an understanding of the altitude and distance you need for each of your turn points. Practice it some with your trainer and on the sim (don't plan to do this for the first time on your first flight with your aileron plane). The base leg is the one that will make all the difference to your approaches. Flying the plane across yourself gives you the chance to really get its altitude right without the time pressure you have when the model is flying towards or away from yourself.

Another little thing about landing - you are by now no doubt used to to whatever roll or other bad behaviour your current plane does on approach. Your new plane will have its own new bad habits. You may find on approach for example that you need to feed in some aileron to counteract a roll etc. Unfortunately sims can't teach you a whole lot about this. However if you want to get a feel for how hard this can be put your trainer up in the air, and then deliberately put her rudder out of trim, just enough so she gently rolls one way or the other. Now land her. Now take off, put the rudder out of trim the other way, and land her. Nasty isn't it? Keep at it.

Okay, takeoffs. I like rolling takeoffs and I don't particularly like hand launching models. If you can find a relatively flat piece of dirt, or even better a hard surface like a carpark (with no cars in the middle of nowhere) then I'd say go rolling takeoff. Rolling takeoffs are much better IMO. Not only are they cooler (I think) but you have more time, and you don't need to compensate for mistakes made by the person who hand launches the model.

Rolling takeoffs wont be new if you had the supercub. If you didn't there is nothing to worry about. Advance the throttle WOT (you can learn finesse with throttle for takeoff later), wait until the tail comes up (assuming you have a tail dragger). Feed in a little up elevator. When the wheels lift off use the elevator to give her a modest amount of up pitch, but make sure you arent' going to stall her. As per the maiden tips (which you should fully review again - particularly setting rates, checking control throws etc) don't try to trim the aircraft just after it leaves the ground. Compensate for the bad trim with the control sticks and keep the plane climbing until you have substantial altitude (minimum 20 metres, ideally more like 30 metres) then start trimming.

If you have to hand launch then ideally get an assistant. Ignore what they say about not throwing the plane up - while throwing up too much is a problem, the difference between throwing level, and throwing down is a subtle one. Aim to throw up at about 20 degrees elevation - almost doesn't matter which plane. Provided there is no danger of anyone losing a finger, throw with 1/2 to WOT. If you have to throw with no throttle then build the throttle up gradualy over the space of one second to prevent torque roll.

The plane needs a decent throw, but try to make sure you that the wrist isn't rolled as the plane is thrown, causing it to start to spiral. If you have to hold the plane behind the wings then use your other hand to support it under the nose (or get your assistant to do that). If you try and just throw it holding it behind the wings the chance of it going staright into the ground (because you are pushing from behind the CoG) is quite high.

When it comes to flying her on your first flight, and all the subsequent flights take the time to learn how she works. Fly her gently and tentatively at first, building up what you ask her to do once you build up your own experience.

Staying Out of Trouble

As alluded to above aileron planes get themselves into different sorts of trouble to RETs (although being too close to the ground remains a universal theme) and need different approach to recovery. For example, early in my Zero's career I busted her up because she had snap rolled onto her back (due to a bad CoG) and I had lost orientation on her. Because she was losing altitude I ended up pulling back on the elevator, which basically made her pull straight into the ground under full power.

The old technique of feeding in a little rudder on the RET is not as effective if we translate it to feeding in aileron on an REAT. Why - because it is symmetrical. If you feed in right aileron the plane doesn't turn right, it rotates clockwise around the fuselage when looked at from behind. Same for left, except it is counter clockwise. If the plane is upside down, it still rolls exactly the same way. Now an RET plane is in a similar boat to some extent, except when an RET plane is upside down it is obvious - the thing is desperately unstable, and is always trying to fall into a stall that it can recover from into level flight. Apart from losing altitude slightly the REAT plane will probably fly fine inverted.

So you need to focus more on your orientation. If you are confused about whether a plane is inverted or not use *a little* (particularly if you are close to the ground) elevator, and reorient based on the result.

You also need to beat your natural compulsion to pull up when you get into trouble. It served you well on your trainer, but you now need to think more. If you pull up after you accidentally over-roll your aircraft all you will achieve is pulling it round into the ground faster. Aileron planes roll out of trouble. Roll until you are not past the 90 degree point, and then start adding up elevator. If you don't have time, then add down elevator while the plane is semi inverted until you have enough altitude to safely roll out. If you really don't have time you may want to add down elevator while you roll her to the full inverted position (it's closer than the upright position yes?) - then once you are safe roll back to normal flight.

However, best thing of all is to stick to the strategies that has served you to this point:

1. Don't let the plane get too close to the ground when it is far away and not easy to determine its orientation by sight.
2. Have a plan for low altitude work - bring the aircraft down, execute the plan and climb back to a safe cruising altitude (5 metres+).
3. Think ahead of the plane particularly if you have a fast model.
4. Concentrate on the orientation of your plane. If you lose track of it, what was it doing last time you had a fix on it. Use small elevator inputs to figure out what it is doing.
   

Simulator Exercises Before You Maiden The New Model:

Fly lots of different aileron planes in FMS or whatever your simulator is. Get a feel for what makes them different. Do plenty of inverted flying (including low level inverted flying). Make sure you have your orientation figured out with respect to the elevator. Do crazy stuff, do low level flying - turn your plane upside down and fly it down the runway 1 metre off the deck etc. Keep in mind the planes in a sim tend to fly much better than real life.

Do a dozen victory rolls so that you don't feel the need to try that on your maiden with your aileron plane, get it all out of your system. You are about to take the next big step - it is going to open a world of possibilities to you but just like when you first started, you need to learn it in stages, and unlike your trainer, your new bird will not be as forgiving.

So, Best of luck


Next Part - Silver Wings (yes the last in the series 8-( )

Back to Learning to Fly

Back to Main

200 FLIGHTS!

Well, it wasn't dignified or graceful, and with her pilot showing the sort of confidence you would expect after smashing two models in the last two weeks the Zero today tentatively flew her 198, 199 and 200th sortie.

The wind was blowing with some nasty gusts, but with more than a week since I had been at the controls I knew it was time to get back on the horse. So we pushed on and remaidened the Zero despite the wind and concerns about her elevator trim.

By and large she flew quite well, although her pilot mucked up every landing, noseing her over at best, landing her in the ditch on one occasion. However, it is clear that her powerplant has been badly damaged by the last crash, and so I've ordered another $15 motor from Taiwa.

In the end it was a low key affair - her 200th flight. I had thought about some extreme things like a little banner she could pull behind her, but in the end she limped through the last 3 flights, and I'm happy to take the runs however they were achieved.

Despite the high wind I also gave my heli a fly. Was a bit silly really and the results are reasonably predictable. However, despite the wind I did manage to keep her airborne for a minute or so on each occasion, running into trouble only when the heli got too far down wind from me (this was a big problem - I couldn't get her to come back from down wind). As she turned away from me and headed downwind I flipped into plane mode mentally and turned her back in a fairly stock aileron/elevator type manuveur. However, in the wind she made it quite clear she didn't have enough authority to come back, turned away and headed away. On both occasions I ditched knowing that I couldn't retrieve the heli in the air.

No damage on the first in. Snapped some undercarriage and damaged the battery tray on the second. Nothing serious really. Am ordering some "Super-skids" from the US - they will take a while to reach here unfortuantely.

Now, as for me..., the two crashes last week seem to have had much more effect on me than I had realised. The Zero, although not quite herself due to the engine issues, was certainly flyable this morning and yet I felt tentative and unsure, my landing approaches were terrible, and the landing that followed was about what you would expect given the build up. There really is something to making sure you stay current with your models and don't let them sit too long, and it is great to always have a plane you can go back to so you can find your way back to the confidence level you had.

I think I had two planes for that purpose - the RV4 and the Zero, and I lost them both on the same day. No matter - I'm confident the way back can be found.

Heli-ish Times

If you've been paying attention then you know that I now have a GWS Mini Dragonfly electric helicopter, which I have been endeavouring to get a handle on at the end of my driveway.

I guess it has already been said many a time, but these are tricky little suckers. Just the amount of stuff you need to track and keep a handle on is staggering. For example, if you've flown fixed wing RC you have some appreciation of the orientation issues etc, but perhaps not much appreciation for how much input from how many controls is required to keep a heli safe.

For example takeoff on one of these little fixed pitch electrics involes getting your head speed to around 95% of lift required for flight, compensating for main rotor torque with a little right rudder, compensating for the heli's tendency to wander to the left with a little right aileron, all the time trying to figure out whether it is going to go backwards or forwards as well, so compensating with elevator (of course in a heli the aileron and elevator do not refer to actual control surfaces - instead the main rotor blade is deflected in that direction to cause the heli to pitch and yaw - this control is known as the cyclic in a heli). At this stage with all four sticks getting active input from you, the little beastie has still not left the ground - and it only gets worse.

Now - because this is a small electric heli it is strongly affected by it's own downforce (so air it blows into the ground that comes back up into its main and tail rotor meaning that if we just try to gradually climb from this point the thing will just buck and scoot all over the place, no doubt ending in tears. At about 50cms (foot and half or so) from the ground the heli gets out of its own rotor wash and you have one less thing to worry about.

This leads to a manuveur which I have heard a number of persons refer to as "punching it" through to an altitude where you get no ground effect.

So, let's recap. Your main rotor has 95% of the thrust it needs for takeoff. You are already giving input to three controls (right rudder, right cyclic and slightly forward cyclic). You know you need to punch the throttle high enough to lift off, compensate for whatever direction the rotor wash chooses to spit your heli out in, establish a altitude and reduce your throttle when you get there, and compensate for the inevitable pitch and roll. Sound like fun? It certainly is challenging.

Orientation on the heli would be the thing I am having the hardest trouble with I think. For example, when the tail spins due to main rotor torque you do find your self fumbling for whether you need left or right rudder etc.

Although I tried a small takeoff (1 inch - straight into the dreaded ground effect) on the first night, on my second day with the heli I was directed to "RADD's school of rotary flight". This useful set of articles gives some guidelines on how to get a feel for the heli on the ground and even suggests going through 9 batteries before you attempt flight. It's really good stuff.

For example, you put your heli in a 1 foot box on the ground and you have to keep it in that box while doing exercises at close to takeoff rotor speed. It gives you a chance on how to learn to anticipate particular forces (like the heli pulling to the left as it takes off).

So, if you have a heli make sure you read through and maybe do all the stuff that RADD suggests before trying to takeoff.

My Zero has been repaired and is awaiting a re-maiden. The bird is certainly showing her age. Her foam seems quite brittle in comparision to when I first go her. But, I'm pretty confident she is going to make her 200 flights.